Sounds like fun! We always stay at a time share and absolutely love having the room to spread out there.
I took three young adults (18, 19, 21) last year in December. It was the first time for the 18 (who is now engaged to my son!). My boys, of course, knew all the things they wanted to do, and we showed her a lot of vloggers.
Their favorite parks in order: HS, EP, MK. We skipped AK bc my brother in law came with us and he also wanted to do Universal. It was a full week!
HS has the Star Wars stuff, which was amazing, Tower of Terror, Rockin' Rollercoaster, Toy Story Midway Mania, Slinky Dog, Mickey Minnie RR. Lines were long even in early December, so we did spend more time in the lines than we would have liked, but we got all the headliners in.
My kids are foodies and they thoroughly enjoyed munching from booth to booth. We rode Test Track, Soarin', Mission Space, Living with the Land (my fave), Nemo & Friends, Grand Fiesta, and Spaceship Earth. They loved shopping in Japan. They loved the little food kiosks for Food & Wine. We enjoyed the merch stands in the lands too.
I did drag them through all the dark rides at MK. It was her first time, she had to do those, right? Truthfully, they loved the Mountains, and Pirates, and the Haunted Mansion; the rest was just humoring the lady that paid for it all.
So, those are my recommendations for going with HS/college age kids.
Oh, we ate one quick service meal in the park each day and then did one drive through meal (dinner all days except EPCOT - we did lunch before the park bc it opened at noon). The parks closed around 7 each night, so that worked out well for us. That is a great way to save some money. You will have a full kitchen in the timeshare, but we don't really cook when we do Orlando theme parks. We do use the heck out of the table though.
Remember that eating can take a lot of time and money, and it is fine to prioritize rides and just eat one off-time meal with lots of snacks. On our 2018 trip, table service for 4 (2 adults, 2 HS kids) ran about $120-150 per meal, and even quick service with desserts to share was about $90 per meal.